where the second term denotes a white noise. Since \(\eta \)  is related
to \(\kappa \)  by Einsten's relation, the motion can be described by
only one parameter \(\kappa \) . This formalism has been very successful in
explaining the \(R_{\scriptscriptstyle AA}\)  and \(v_2\)  of \(D\)  mesons
[1]}. It is, however, difficult to calculate \(\kappa \)  from
thermal QCD: the leading order (LO) result [2]}, [3]} is far
too small for phenomenology. Perturbation theory for this object
is also quite ill-behaved: for temperatrues of interest, the next to
leading order (NLO) result is an order of magnitude larger than LO [4]}.
A nonperturbative estimation of the diffusion coefficient is therefore
called for.
